IODP-MSP drilling and
logging contractor: ESO
Hole: M0028A
Expedition: 313
Location: New Jersey (NW Atlantic)
Latitude: 39°33.9427′ N
Longitude: 73°29.8348′ W
Logging date: June 05, June 16-18, 2009
Sea floor depth
(driller's): 52.42 m DRF
Sea floor depth (logger's): 52.00 m WRF
Total penetration: 668.66 m DSF
Total core recovered: 385.50 m (80.82 % of cored section)
Oldest sediment recovered: Early Miocene
Lithologies:
Clays to gravels
The logging data was
recorded by the
Tool
string
|
Run/Pass
|
Top depth (m WSF)
|
Bottom depth (m WSF)
|
Pipe depth ( m DSF)
|
Notes
|
1. ASGR
|
Through pipe
|
0
|
389.56
|
~404
|
Merged with run 3 |
2. VSP
|
Lower
|
395.45
|
667.94
|
~404
|
1.83 m spacing |
3. ASGR
|
Lower
|
324.13
|
670.20
|
~669
|
Merged with run 1 |
4. DIL45
|
Lower
|
424.86
|
648.5
|
~426
|
Merged with run 9
|
5. EM51
|
Lower
|
425.40
|
657.00
|
~425
|
|
6. ABI40
|
Lower
|
426.30
|
637.97
|
~425
|
|
7. VSP
|
Middle
|
402.15
|
656.36
|
~396
|
1.83 m spacing
|
8. VSP
|
Middle
|
20.05
|
431.53
|
~396
|
1.83 m spacing
|
9. DIL45
|
Middle
|
395.30
|
489.19
|
~396
|
Merged with run 4 |
10. ABI40
|
Middle
|
396.04
|
429.17
|
~396
|
|
The depths
given in the table are for the processed data. The raw data may contain extra
data within the pipe: this data has been removed from the processed data files. The depths
in bold refer to top and bottom depths of files before merging
(i.e. the top and bottom depth of the final merged files are not in bold).
A complete
list of tool and log acronyms is available at http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-acronyms.html.
The logged intervals in each borehole are described as lower, middle and upper. These do not match across boreholes either in terms of depth or sequence boundary. In any case, logging has not been carried out in more than three stages. These intervals can be seen at
http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-ops-summary.pdf.
General Information
The suite of tools available for logging on Expedition 313 consisted of spectral gamma ray (ASGR), velocity (2PSA), conductivity (DIL45), acoustic borehole imaging (ABI40) and magnetic susceptibility (EM51) measurements. s. Each tool was run separately. Upon coring completion, the spectral gamma log was acquired through drill pipe. Subsequently the hole was conditioned with drill mud. The unfavorable borehole conditions required logging openhole in separate intervals. Difficulties pulling pipe and the development of bridges affected the ability to log certain sections of the boreholes (especially the upper, more unconsolidated sandy sections). The logger’s zero depth position was taken as the top of the drill pipe. Discrepancies in depths between initial zeroing and zeroing on removal of the tool were generally less than 0.5 m. The depths in the table are for the processed logs (after depth shift to the sea floor). Generally, small discrepancies exist between the sea floor depths determined from the downhole logs and those determined by the drillers from the pipe length. Typical reasons for depth discrepancies are ship heave, wireline and pipe stretch, tides, and the difficulty of getting an accurate sea floor from the 'bottom felt' depth in soft sediment. For New Jersey, logging was done from a platform and so there was no ship heave to account for.
Hole M0028A logging
Through-pipe gamma ray measurements were acquired over
the entire borehole in two stages. VSP measurements were also acquired over the
entire borehole through pipe and in open hole in the lower and middle sections.
As in the two other boreholes, drilling began using PQ sized pipe, which was subsequently changed to the smaller diameter HQ
pipe at ~400 m. This meant that logs in the lower interval had to fit through
a smaller diameter pipe; for this reason, the 2PSA sonic tool was not used, the centralisers being too large to
fit through the HQ pipe. Open
hole logging operations took place in three stages:
Lower section (425 to 669 m WSF): in this section, borehole conditions
were good and the conductivity, magnetic susceptibility and acoustic image
tools were run. Only 10 m at the base of the hole could not be logged due to
infilling. The conductivity tool was blocked by a bridge that formed at 348.6
m WSF. The two subsequent tools managed to pass this bridge.
Middle section (396 to 430 m WSF): this section was expected to be
unstable and sandy and to collapse once the HQ pipe was pulled. However, when
the VSP tool reached the base of the PQ pipe at the start of VSP acquisition
the tool managed to go below the base of the pipe. Subsequently both conductivity and acoustic logs
were able to be run for an additional ~20 m of previously unlogged borehole. A
large overlap in the conductivity log enabled precise merging of the logs in
the middle and lower sections.
Upper section (above 396 m WSF): logging was planned in this section but could not be carried out because the PQ pipe
was stuck.
Depth
shift: The original logs were first corrected for the
difference in zero tool depths and the difference between logger’s and
driller’s zero points (if applicable). For hole M0028A the logger’s zero point was located beneath the driller’s
zero in order to make the tool entry and exit point easier to access. See http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-depth-layout.pdf . Finally, logs
were depth shifted to the sea floor using the driller’s depth to seafloor
(-52.42 m below rig floor). The driller’s distance to seafloor was chosen
as the reference depth because for each hole this fell within the range of the
depth to seafloor given by the gamma ray log. The gamma ray log through pipe was
taken as the reference log (continuous) and where appropriate other logs were
depth-matched to it. For M0028A the
magnetic susceptibility log required a small linear shift down (0.33 m) to
match the spectral gamma log. The log depths are
therefore m WMSF.
Data merges: Where there was an overlap the data was merged. Due to the usually excellent match in the overlap section, the data in the merged section was averaged. In hole M0028A the following logs were merged:
DIL45 middle section (run 9) / lower section (run 4)
ASGR through pipe (run 1) / lower section (run 3).
The
acquisition of acoustic borehole images occurred in several files due to their
size (see image notes for more details).
Environmental
corrections: None.
Acoustic data: No acoustic tool was run in this hole.
Spectral gamma ray: Gamma ray logs recorded through drill pipe should be used only qualitatively due to attenuation of the incoming signal.
The quality
of the data is assessed by checking against reasonable values for the logged lithologies, by repeatability between different passes of
the same tool or down and up logged intervals, and by correspondence between
logs affected by the same formation property (e.g. the resistivity log should
show similar features to the acoustic log).
The quality of the ASGR Spectral Natural Gamma data is
directly related to lithology in combination with
logging speed. Where counts are lower the reliability of the statistical
function used to separate raw counts into values of naturally
occurring radioactive elements [potassium (K), uranium (U) and thorium
(Th)] is degraded. Negative values are indicative of incorrect statistics; when this is the case, K, U and Th values at that depth
has been replaced by a null (-999.25). Gamma ray logs recorded through drill pipe
should be used only qualitatively due to attenuation of the incoming signal.
A wide and/or
irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall. Hole diameter was calculated from the acoustic imageing
tool (ABI40).
Whenever possible, data was acquired downlog, uplog and through the pipe. In this case the uplog is
usually the final output. The data recorded within the pipe are usually removed from the
final log. This data has been retained in the original data files.
A null
value of -999.25 may replace invalid log values.
Additional
information about the drilling and logging operations can be found in the
Operations section of the Site Chapter in IODP Proceedings of Expedition 313.
For further questions about the data, please contact:
Jennifer
Inwood
University
of Leicester
Phone: 011-44-116-252-3327
Fax:
011-44--116-252-3918
E-mail: iodp@le.ac.uk
Johanna Lofi
University
of Montpellier 2
Phone: 033-
467-149- 309
Fax: 033- 467-
143- 244
E-mail: iodp@le.ac.uk
For any web
site-related problem please contact:
E-mail: logdb@ldeo.columbia.edu